9/29/14. Amanda M. Lauer, Dept. of Otolaryngology- HNS. From Signal Detection Theory and Psychophysics, Green & Swets (1966)

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1 Amanda M. Lauer, Dept. of Otolaryngology- HNS From Signal Detection Theory and Psychophysics, Green & Swets (1966) SIGNAL D sensitivity index d =Z hit - Z fa Present Absent RESPONSE Yes HIT FALSE ALARM No MISS CORRECT REJECT Signal Detection Theory Abdi (2009) d =1.4 Increasing discrimination d =0.9 d =1.4 d =0.9 Response bias Not discriminable From Steven s Handbook of Experimental Psychology (2002) with modifications From Steven s Handbook of Experimental Psychology (2002) with modifications 1

2 On to auditory filters and masking Lauer et al. (2011) Output () How do you estimate auditory filter size and shapes using psychphysics? Helmholtz (1863), and later Fletcher (1940), hypothesized that the auditory system functions as a set of overlapping bandpass filters Resolvability of different frequencies (frequency selectivity) depends on the width of these filters The presence of a competing sound(s) makes it more difficult to detect or discriminate a target sound, particularly when they overlap in time or frequency. Energetic masking (depends on stimulus spectrum, intensity, temporal characteristics) Informational masking (other factors; attention?) Simultaneous Forward Backward Masker Signal Time 2

3 Neural swamping or suppression? Swamping: masker produces activity in a channel, activity added by signal undetectable Suppression: activity produced by masker actually suppresses response to signal Both? Threshold for a tone signal increases as bandwidth of a noise masker increases up to a certain point, then threshold remains constant. Critical Bandwidth (CB) Data from Schoonvelt & Moore (1989) You can also estimate the CB indirectly by measuring the threshold of a tone in broadband noise. Assumptions: 1. Only the narrow band of frequencies surrounding the tone (within CB) contribute to masking 2. When the noise just masks the tone, the power of the tone, P, divided by the power of noise inside the CB (W) equals a constant K. Lauer et al The ability to detect signals in noise worsens with cochlear damage, and CRs increase. CR formula: W=P/(K*N 0 ); K=1 (approx.) at threshold, so W=P/N 0 simultaneous masking, using sinusoidal signals at 10 SL. For each curve, the solid circle below it indicates the frequency Other psychophysical estimates of auditory filters & frequency selectivity Absolute thresholds Signal Signal is fixed at a low sensation level (~10). Masker level and frequency (tone or narrowband noise) is varied. The level of masker required to just mask the signal is determined. From Moore (2003) Psychology of Hearing. 3

4 PTCs measured using non-simultaneous masking are sharper. Suppression in simultaneous masking. From Moore (2003) Psychology of Hearing. Measure threshold for signal in noise with spectral notch centered around tone signal frequency. Increase notch width until threshold is no longer masked. Figure from Lina & Lauer (2013). Originally conceived of by Patterson. Calculate filter shape from masked thresholds. Calculate Equivalent Rectangular Bandwidth (ERB) to provide a convenient single estimate of width of filter (bandwidth when power of filter response has fallen by factor of two (3 ). Auditory filters broaden with level. Data from Rosen & Baker(1994) Figure from Lina & Lauer (2013). Originally conceived of by Patterson. Masker: narrowband noise centered at 410 Hz Measure detection thresholds for tones in narrowband masker with constant level. Upward spread of masking: ~ linear growth of masking for frequencies near tip; nonlinear growth for frequencies far from tip. Egan & Hake (1950). Excitation pattern calculated for a 1000 Hz tone based on notched noise data Moore & Glasberg (1983) 4

5 9/29/14 Cochlear damage results in flattened, broadened masking (excitation) patterns Lauer et al Lauer et al Auditory filters are broadened in ears with sensorineural hearing loss (frequency selectivity is impaired), especially on low frequency side. Glasberg & Moore (1986). PTCs broaden with cochlear damage; sharp tip is lost Temporal effects on masking Increased susceptibility to masking, especially for maskers with lower frequencies than the signal. Issue: cannot test hearing-impaired subjects at lower stimulus levels where filters are normally narrower. Rate of recovery is slower for impaired listeners, but the difference is reduced when compared at equal sensation levels. Caveat: many of these studies were completed in older hearing- impaired adults, and age may compound the effects of temporal manipulations. Time Increasing the delay between masker and stimulus improves detectability (reduces masking). Depends on level, frequency, duration. Glasberg et al Jesteadt et al

6 Cochlear damage can completely disrupt the phase response of the basilar membrane. Lauer et al. (2006) Phase (and phase delay) of masker components affects detectability of a signal in addition to its spectral components. This is subject to nonlinear processing in mammalian ears. Lauer et al. (2009) Auditory filter bandwidth determines frequency selectivity. There are many ways to estimate filter bandwidth & shape using masking tasks. Filters broaden with hearing loss. Masking effects can be very complex (time, frequency, level effects). Cannot rue out central auditory processes affecting the psychophysical tasks! Increased susceptibility to masking Reduced ability to resolve components in sounds that are close in frequency Reduced effect of different stimulus phase spectra = Impaired speech perception 6